Here's the real scoop...
A standard USB port on a computer can supply up to 500 mA. As long as your batter charger lists an output less than that, you'll "probably" be ok plugging it into the computer.
It's still a bad idea, and here's why:
These chargers are all designed by the cheapest engineer that could be found, produced in the cheapest factory that could be found, with the cheapest materials that could be found, etc... See where this is going?
If something does happen to go wrong with it, do you want it to fry the motherboard in your $500 computer or fry the 4 dollar wall wart that you could have used with it?
USB ports in computers are meant for transferring data. They weren't designed to be bulletproof power receptacles. Some high end computers have protection circuitry built into the ports that would prevent damage if an accessory went bad, but those computers aren't exactly sold at best buy.
It costs like five bucks to play it safe. Just play it safe.
Having said all that, I typed all that while my KGO charger was plugged into the USB port on my laptop. It's like car insurance. If you really want to play the odds, then the odds are that you can drive without insurance for many years with no problems. But when you do finally have a problem, good luck finding a single soul that has even a tiny bit of sympathy for you.